Vitreous enamel



3,055,7 62 VITREDUS ENAMEL Lewis C. Hoffman, Scotch Plains, N.J., assignor to E. I. du

Pont de Nemours and Comp any, Wilmington, DeL, a corporation of Delaware M01 percent to 7 0 to 4 This vitreous enamel frit may without material disad- ZnO CdO Drawing- File}! 1960: 74,212 vantage contain a total of up to mol percent of other 3 mmms' (fl'm5 49) oxides sometimes contained in enamel frits, provided, This invention relates to an improved vitreous enamel, however, that not more than 4 mol percent thereof be and more particularly it relates to a vitreous enamel havcomposed of a single such other frit ingredient. ing a marked superiority for use in the application of It has been found in accordance with this invention vitreous enamel labels on glass bottles or other glass sur- 10 that small amounts of PbF in combination with small faces. amounts of will lower the maturing temperature of Vitreous enamel labels and colored indicia or other the enafrntell fritslwithout matenallly ifncreasli/iiig the coeililiglass coatings have for some time been applied to bevercient o erma expansion of t 6 mt. oreover, t e age bottles and other glass surfaces. Such glass coatings added PbF was found capable of dissolving greater are necessarily required to be composed of vitreous amounts of ti}; refractory congnonzeigs in 311s egamel in a enamel compositions that will fuse and coalesce at a Elv n tim at is to say, Ti r 2 an i 2 contents temperature below that at which the underlying glass of a frit are dissolved more rapidly by the presence of surface may become soft and deform. They must there- 'Tz than 111 the Presence Of Other T s is of fore be capable of firing at a temperature of 640 C. or decided advantage because the glass melting process is a below. Moreover, they must have a slightly lower cocompetiltioi betweer raplid solution, volatility of ingrediefiicient of thermal expansion than the bottle or other ents an re ractory isso ution. glass surface on which they are to be adhered to prevent The combination of PbF with NaF produces superior the development of highly objectionable stresses upon results to the use of PbF alone or to the use of NaCO cooling the glass from the firing temperature. A linear or NH F in combination with PbF The combination coefiicient of thermal expansion of the glass overlayer of of PbF and NaF produces a frit having a 10 C. lower from about 2 to 7 10- cm./cm./ C. below that of the melting point than the other said combinations in similar underlying glass surface is considered to be satisfactory. amounts without sacrifice of chemical resistance or ex- Beverage bottles are, for the most part, used for sevpansion coefiicient. eral trips. That is, after one use they are washed, refilled The other listed ingredients are also considered to be and rescaled. They undergo an average of about trips 30 important to obtaining the above-described balanced in this manner and some bottles are subjected to as many characteristics. In the enamel frit compositions of this as 100 trips. Each time abottle is washed it is exposed to invention the SiO contributes to low thermal expansion an alkaline detergent solution at an elevated temperature. b t m st be regulated to prevent high maturing temperas h l ti usually containing phosphate i e ture. The B 0 lowers maturing temperature at a sacriquite corrosive of the enamel labels. The vitreous enamel fice f chemical resistance i a gradual increase i rto be used for such labels must therefore be highly rema1 eXPaHSi0I1- Pbo lowers maturing temperature at a sistant to alkaline detergents. sacrifice of chemical resistance with a gradual increase in Again such bottles are often subjected to fruit acids thigmal expansion. 1211 llowers maturing emperature wi an increase in t erma ex ansion. 1 increases i m c a r p a clii ri g c b n iil ei s T h sit ri o uf fa c a l e iiaiife l s alkali resistance and maturing temperature. 2 TiO inmust therefore al o hav gr ate than usual a id re i tcreases acid resistance and maturing temperature but has ance. a tendency to crystallize from the enamel on firing to It is an object of this invention to produce an improved Produce an unpleasant yellow shade. ZnO tends to minivitreous enamel frit suitable for use as a label on glass mlze thls tendency without detrimental effect on the other beverage bottles. properties. The CdO serves to prevent the reaction of It is a further object to provide a vitreous enamel frit PbO with sulfide pigments such as CdS yellow or suitable for use as a label on glass beverage bottles and Cd(S Se) reds, where used in colored labels, to form having improved melting point, expansion coeflicient, and black PbS. It is critical in accordance with this invenalkali and acid resistance characteristics. 5O tlon that the PbF content and the NaF content be pres- Other ob ects of the invention W111 appear hereinafter. ent in the enamel composition in the mol percentages I These objects may be accomplished by providing a above set forth. vitreous enamel frit composition comprising, The following three tables disclose sixteen specific ex- Mol percent amples of compositions coming within the scope of the SiO 37 to present invention. Table I discloses the compositions in B 0 5 to 10 mol percent, and Table II discloses the same examples PbO 22 to 30 expressed in weight percent for purposes of comparison P bF 3 to 8 with the prior art compositions expressed in weight per- NaF 7 to 14 cent. Table III again discloses the same 16 compositions ZrO H06 in weight percent of the batch ingredients from which T10 0 to 8 the compositions are prepared.

TABLE I Melted Compositions, M ol Percent 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Ranges TABLE II Melted Compositions, Weight Percent 12345678 '10111213141515 TABLE III Batches, Weight Percent 20.4 22.3 21.0 23.5 23.5 25.4 10.4 23.7 22.3 21.5 24.5 20.5 21.5 24.5 24.5 25.2 8.3 8.3 0.0 5.5 5.5 5.5 0.0 5.7 5.7 5.5 5.5 5.5 5.5 5.5 5.5 8.3 50.1 48.2 40.0 51.3 47.7 45.4 47.3 44.5 50.0 40.3 50.3 54.2 52.3 45.5 45.5 50.1 8.2 8.2 8.0 8.3 8.5 8.5 8.1 14.7 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.2 3.0 3.0 4.3 3.0 3.0 3.0 3.8 3.9 4.0 3.0 3.0 3.0 3.0 3.0 3.0 2.0 4.8 4.8 4.8 4.9 4.0 5.8 4.8 4.4 4.4 4.0 4.0 4.0 3.0 5.8 4.0 1.0 2.0 2.0 2.0 1.5 3.4 2.0 2.0 3.4 1.5 1.5 1.5 3.4 4.4 5.3 2.4 1.4 1.4 4.0 3.8 3.0 As above stated, the enamels of this invention must 1350 C. Such times and temperatures can only constihave a maturing temperature of not to exceed 640 C. tute a general guide since the time required at a given (1184 F.). T he compositions listed in the tables have temperature is also a function of the size of the batch and maturing temperatures between about 570 and 620 C., the particular heat transfer conditions of the furnace. thermal expansions between about 85 and 90 10- cm./ Crucible temperatures may vary from 1000 C. to l500 cm./ C. and outstanding chemical resistance. All of C., as desired. these enamels will resist the attack of an aqueous alkaline Upon complete dissolution of the batch ingredients l tion t i i 9% N QH d 1% N 1 0 t 80-90." the molten batch is fritted in a known manner by pouring C. for a period exceeding 24 hours. This method of testthe same into water which shatters it into small pieces ing the chemical resistance of enamels is commonly used forming thereby the enamel frit. Low temperature fritting as an accelerated test for applied vitreous enamel labels With air or other means as employed in the art may for beverage bottles. Enamels heretofore used in the arts alternatively be used if desired. for such enamel labels failed to withstand the above test The frit may, if desired, be dried before grinding to for a period of over 22 hours. The compositions of this form the enamel. The grinding is usually carried out in invention have outstanding resistance to acids. They a ball mill at which point pigments or coloring matewill show no visible attack on exposure for 15 minutes to rials or other additives are usually added. For example, 10% citric acid at room temperature. This acid resistivity 10% 0f z p q ing pig may e add d to the test is also a common accelerated test for the acid duraffill Composition of Example The grinding is usually bility of beverage bottle labels and for the weatherability carried out with sufiicient water or other liquid to proof enamels for a hitectur l glass duce a pourable or sprayable product. The resulting The enamels of this invention may be used in enamelffit Slurry y be p y directly Onto the glass bottle ling or glazing glass substrates having thermal expansions other glass Substrate- Th sprayed-on coating is then of about 85 to 95 X 10 cm./cm./ C. This includes most dried d fir of the soda-lirne-silicate glasses commonly used for If desired the enamels may be milled dry or dried bottles, window and plate glass. after Wet milling and later mixed with a desired binder The enamel compositions of this invention may be Vehicle whereby to apply the enamel to a surface by ground to a fine state of subdivision, intimately mixed spraying, dipping, brushing or stenciling. As an exwith ceramic pigment particles, applied with the help of a ample of a suitable vehicle for the enamel application, binder onto the surface of a glass to be enameled and one compound of methyl cellulose 0.75%, sodium chlofired to fuse the glass enamel composition to the glass subrid 1%, octyl alcohol 0.05% and water 98.2% (all parts strate, all in amanner well-known in the art. by Weight) may be used. Another useful vehicle con- In preparing these frit compositions complete dissolu- SiSts of commercial water glass (sodium silicate solution) tion of the batch components must be attained and usually 0.4% sodium fluosilicate 0.4% and water 99.2%. A suitspecial care is taken to see that the ZrO is dissolved. To able vehicle for applying the vitreous enamel by the squeeascertain the completeness of melting, samples of the melt g t n il appli ation procedure is one composed of may be taken and examined in a known manner for deethyl cellulose (25 C.P.S. viscosity grade) 4% soya tection of undissolved material. The crucibles used for cith n 0.25%, and terpineol 95.75%. batch dissolution of the compositions may be composed It is desirable to apply the enamel to the surface of the of fireclay-grog, kyanite, platinum or any other commonly glass substrate in any manner that will provide a uniused crucible material. form and smooth coating before firing. The thickness The time required for dissolution of the batch ingrediof the coat may be varied within wide limits according to ents (usually determined by the time necessary to disthe type of effect desired, e.g. 15 to 30 grams (based solve the Z0 is a function of the temperature of the on the dry Weight of enamel) per square foot.

melting operation. A 100 gram batch of the composition shown in Example 1 of the tables when placed in a platinum crucible and melted in an electrical resistor furnace will melt in minutes at 1200 C., in 40 minutes at 1250 C., in 36 minutes at 1300 C. and 22 minutes at After application of the enamel to the substrate, the composition is fired in a suitable furnace in order to fuse the powdered enamel to a continuous glossy coating. The firing conditions are not critical, except that the article must be brought to a temperature high enough to melt the enamel but not high enough to materially deform the glass substrate. The temperature necessary depends to some extent upon the particular composition of the glass substrate as well as the enamel. Usually a temperature of between 900 F. and 1200 P. will be suitable. It is merely necessary to keep the coated article at the selected temperature for a few minutes to permit the enamel to fuse completely to a uniform, adherent, vitreous layer.

The enamel compositions of this invention, as compared to vitreous label enamels heretofore known, have a higher chemical resistance to alkalis and acids and have a lower maturing temperature as a result of which they can be applied and fired with good adherence and without endangering the simultaneous melting of glass substrates.

Parts, proportions and percentages as used throughout the specification and claims refer to parts, proportions and percentages by weight except where mol percentages have been specifically referred to.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

I claim:

1. A vitreous enamel frit suitable for use as vitreous enamel labels on glass substrates having a maturing temperature below 1184 F. and a thermal expansion of between 85 and 90 10- cm./cm./ C., at least 90 mol percent of the frit consisting of M01 percent SiO 37 to 50 B203 t0 PbO 22 to 30 PbF 3 to 8 NaF 7 to 14 Zr0 1 to 6 32 CdO 0 to 14 and up to mol percent of said frit consisting of other known frit ingredients with not to exceed 4 mol percent of any one known ingredient, all of said oxides being melted into said enamel compositions.

2. A process for applying a vitreous enamel layer on a glass substrate which comprises fusing thereon a vitreous enamel having a maturing temperature below 1184" F. and a thermal expansion of between 85 and 90 10- cm./cm./ C., at least 90 mol percent of the frit consisting of M01 percent SiO 37 to B 0 5 to 10 PbO 22 to 30 PbF. 3 to 8 NaF 7 to 14 Zl'Og 1 t0 6 Ti0 O to 8 ZnO 0 to 7 CdO 0 to 14 and up to 10 mol percent of said frit consisting of other known frit ingredients with not to exceed 4 mol percent of any one known ingredient, all of said oxides being melted into said enamel composition.

3. A glass substrate containing fused to the surface thereof a vitreous enamel having a maturing temperature below 1184 F. and a thermal expansion of between and l0 cm./cm./ C., at least 90 mol percent of the frit consisting of and up to 10 mol percent of said frit consisting of other known frit ingredients with not to exceed 4 mol percent of any one known ingredient, all of the said oxides being melted into said enamel composition.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,044 Deyrup Sept. 9, 1941 2,278,868 Deyrup Apr. 7, 1942 2,356,317 Harbert et a1. Aug. 22, 1944 2,413,549 Deyrup Dec. 31, 1946 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,055,762 September 25 1962 Lewis C. Hoffman It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columns 1 and 2, TABLE I, opposite "S10 column 13, line 1 thereof, for "72.6" read 42,6

Signed and sealed this 6th day of August 19630 SEAL) .ttest:

RNEST w. SWIDER DAVID LADD .ttesting Officer Commissioner of Patents 

1. A VITREOUS ENAMEL FRIT SUITABLE FOR USE AS VITREOUS ENAMEL LABELS ON GLASS SUBSTRATES HAVING A MATURING TEMPERATURE BELOW 1184*F. AND A THEMAL EXPANSION OF BETWEEN 85 AND 90X10-7 CM./CM./*C., AT LEAST 90 MOL PERCENT OF THE FRIT CONSISTING OF 